In wireless voice and data communications systems, including mobile systems having multi-band and multi-system capabilities, reducing the physical size of the radio transmit/receive devices, such as mobile cellular telephones, is an important design consideration.
For radiating/receiving antennas that are buried within the radio-devices (i.e. internal-antennas), the need to reduce the physical size of the radio-devices imposes a severe constraint on the physical volume within each radio-device that is allowed for an internal-antenna and its radiating/receiving element (hereafter called radiating element).
A planar inverted-F antenna (PIFA) is commonly used as a radio-device's internal-antenna. A reduction in the physical volume that is available within the radio-device for housing the PIFA's radiating element results in a negative impact on both the bandwidth and the gain of the PIFA.
In addition, with a trend toward restricting the height of such internal-antennas to from about 3 millimeters (mm) to about 5 mm, it is difficult to provide a multi-band PIFA that has a requisite bandwidth and gain.
Although it may be that a PIFA design that is associated with a photonic band gap (PBG) structure can be used to overcome the negative effects of such a reduced height, the associated geometric configuration that is imposed by the design of a ground plane for such a PIFA that includes the PBG phenomenon is difficult.
Therefore, antenna configurations that feature some or most of the advantages of a PIFA, and yet require a smaller volume than a conventional PIFA, are of great value to antenna and system designers.
The present invention makes use of printed circuit techniques. The use of printed circuit techniques in antennas is known, as shown for example in U.S. Pat. Nos. 5,754,145, 5,841,401, 5,949,385, 5,966,096 and 6,008,774, incorporated herein by reference.
In an embodiment of the invention wherein a multi-band printed-antenna (under unbalanced conditions) has its radiating element formed on a printed circuit board (PCB) so as to be coplanar with, but physically spaced from, a ground plane element that is also formed on the PCB, the printed-antenna resembles a multi-band, printed, inverted-F antenna (printed-IFA).
A single band IFA is described by C. Soras et al. in an article entitled “Analysis and Design of an Inverted-F Antenna Printed On a PCMCIA Card for the 2.4 GHz ISM Band”, IEEE APS Magazine, Vol. 44, No.1, February 2002, pp. 37-44.
In an embodiment of the invention wherein a multi-band printed-antenna has its radiating element located on the top surface of a hollow, four-sided and box-like dielectric carriage that is supported by a PCB, such that the radiating element is parallel to, but is spaced from, a ground plane element that is formed on the PCB, the printed-antenna resembles a meander-line antenna.
Prior art meander-line antennas provide for the meander-line radiating element to be placed on a PCB itself, whereas this invention provides that the radiating element of the printed-antenna is located on a separate dielectric surface that is provided at a desired height above, and laterally spaced from, the ground plane element. For example the ground plane element is placed on a PCB that is located within a radio device, this PCB also incorporating the circuit components of the radio-device. For example, the ground plane element also functions as a ground potential for the radio-device's communication circuitry.
Embodiments of the present invention provide that the generally flat radiating element is located on a different plane than the generally flat ground plane occupies, these two planes being generally parallel, and embodiments of the invention provide for the shorting of a point on the radiating element to a point on the ground plane
Unlike prior known meander-line antennas, the present invention provides a dielectric carriage whose sidewalls provide for the reactive loading (for example capacitive loading) of the printed-antenna's radiating element. This reactive loading is provided by one or more conductive metal strips or plates that extend downward from one or more edges of the meander-line radiating element, generally flush with the outer surface of one or more sidewalls of the dielectric carriage. This reactive loading aids in lowering or controlling the resonant frequency of the printed-antenna, without increasing the physical length of the printed-antenna's meander-line radiating element.
An advantage of the present invention is that a physically compact, low profile, simple geometry, single-feed, planar and printed-antenna in accordance with the invention provides multi-band performance with satisfactory gain and bandwidth.
Structural configurations of various embodiments in accordance with this invention are cost-effective and easy to manufacture.
The requisite bandwidth performance of multi-band, planar and printed-antennas in accordance with this invention is realized without requiring the use of an impedance matching network that is external to the printed-antenna.
In spite of the constraints on an internal-antenna's geometry that is provided by the manufacturers of radio-devices such as cellular telephones, this invention provides viable printed-antenna embodiments that are physically compact, that provide for a single-feed, that are multi-band, and that provide satisfactory gain and bandwidth performance.